Near-Field Radar Principles and Low Contrast Target Imaging Methods

雷达正在成为一种广泛应用的传感器技术，用于现代应用，例如物联网（IoT）基于位置的服务，手势交互以控制可穿戴电子设备-虚拟工具，以及作为医疗诊断，监测种子发芽，油井监测和隧道掘进机引导和控制的成像工具。这些应用大多是非常短的距离，有时在几厘米（近场），并要求高精度的测距和图像分辨率。在雷达方法中，反射波的旅行时间被考虑用于传感和成像。在测量中，雷达和目标被定位在很远的距离。这种成像方法的基本限制是衍射极限。为了提高图像的分辨率，在绕射极限以上，需要从目标附近捕获一部分能量，这部分能量被定义为雷达与目标之间的近场相互作用，在雷达近场中，电场和磁场无论在频域还是在时域都是非常复杂的。在时域雷达的近场，脉冲波形不稳定，脉冲传播速度超过光速。为了利用近场相互作用提高雷达的探测和成像能力，需要深入了解近场原理和成像算法，研究近场雷达的原理和理论框架，近场成像方法，实现各种成像应用。该研究的目标是了解时域近场雷达的物理特性，并开发用于短距离应用的雷达系统，以实现超过衍射极限的图像分辨率。该研究的应用是（i）开发利用雷达与目标的近场相互作用来监测窄金属管道和油井威尔斯中的小穿孔的技术，（ii）开发对诸如电子元件、简易爆炸装置（IED）及其雷管的非线性目标成像的技术，（iii）发展微波成像技术（MIT），以成像介电常数差异小于10%的低对比度介电不连续性。通过提高雷达成像分辨率超出传统预期，同时具有成本效益，易于操作，并为各种应用提供近实时成像，从而实现了现场雷达成像和显微技术。它们可以为医疗诊断工具、控制可穿戴电子设备的虚拟工具以及用于现代物联网解决方案的传感器带来革命。

Radar is becoming a widely applied sensor technology for modern applications such as the Internet of Things (IoT) location based services, hand gesture interaction to control wearable electronics - virtual tools, and as an imaging tool for medical diagnosis, monitoring seed germination, oil well monitoring, and tunnel boring machine guidance and control. Most of these applications are very short range, sometimes within a few centimeters (near-field), and demand high precision ranging and image resolution.In radar methods, travel time of the reflected wave are considered for sensing and imaging. In measurements the radar and target are positioned at a far distance. The fundamental limitation of this imaging method is diffraction limit. To improve the image resolution beyond the diffraction limit, some of the energy from the target proximity should be captured which is defined as a near-field interaction between the radar and the target.In radar near-field the electric and magnetic fields are very complex either in the frequency domain or in time domain. In the near-field of a time domain radar the pulse shape is not stable, and the pulse propagation is faster than the speed of light. To take the advantage of near-field interaction to improve the detection and imaging capability of the radar, a thorough understanding of the near-field principles and imaging algorithms are needed.My research program will develop principles and theoretical framework for the near-field radars, methods for near-field imaging, and implement various imaging applications. The goals of the research are to understand the physics of time-domain near-field radars and to develop the radar systems for short range applications that achieve image resolutions beyond the diffraction limit. The application for the research are to (i) Develop a technology, by exploiting near-field interaction of the radar with the target, to monitor small perforations in narrow metal pipes and oil wells, (ii) Develop a technology to image the nonlinear targets such as electronic components improvised explosive devices (IEDs) and their detonators, (iii) Develop microwave imaging technology (MIT) to image low contrast dielectric discontinuities where the difference in dielectric constant is lower than 10%.This research bridges the technology gap between the traditional far-field radar imaging and microscopic techniques by improving the radar imaging resolution beyond the traditional expectations, while being cost effective, easy to operate, and providing near-real time imaging for various applications. They can bring revolution in medical diagnosis tools, virtual tools to control wearable electronics, and sensors for modern Internet-of-Things based solutions.